The invention relates to procedures and compositions for determining the performance of paper coating apparatus for ink jet printers.
Ink jet printing methods use printheads having orifices which eject ink droplets onto a print medium. For higher quality, higher resolution printing applications, the orifices of the printheads have been increased in number and their diameter significantly reduced in size. Accordingly, for full color printed images, inks are formulated to include dyes and/or pigments and various carriers and/or solvents which are resistant to drying or otherwise clogging the nozzle holes of the printhead. Such ink formulations, however often adversely affect the properties of the ink deposited on the print medium resulting in longer drying times and/or color mixing or bleeding of the images resulting in poorer quality images.
Print media used with ink jet printers include a wide variety of materials with the most widely used being cellulosic print media. Cellulosic webs used as print media are made by conventional paper making techniques wherein a fibrous pulp is deposited on a wire screen and dried to form a web. Accordingly, the webs contain minute pores or voids between the cellulosic fibers for absorption of liquids therein. The porosity of the webs may be changed by use of specialty coatings such as clays and the like which may change the hydrophilic properties of the webs so that the webs absorb or repel aqueous and/or organic fluids which may be used as carrier fluids in ink formulations.
It is desirable for only the carrier fluid of the ink formulation to penetrate into the web thereby depositing colorant on the outer surface of the web. Balancing the properties of the ink formulations so that the formulations are adaptable for use with a wide variety of print media is extremely difficult. It is even more difficult to provide ink formulations which may be used on uncoated or plain paper webs. In an effort to improve the print quality, the webs or print media are preferably coated with materials which improve the drying time and penetration of the ink. In one system, the webs are preferably coated immediately prior to printing. However, if the coating is not uniformly applied to the print media during the coating process, the image quality may suffer. Accordingly, a need exists for methods and compositions which can be used to assure uniform coating of the webs prior to printing.
With regard to the above and other objects and advantages thereof, the invention provides a test fluid for detecting coating flaws in a coated web and a method for testing a web coating system. The test fluid includes, water, a polyol, a surfactant, a radiant energy activated tracer compound and an organic solvent selected from the group consisting of an alkylene glycol and a dialkylene glycol.
In another aspect the invention provides a method for testing a web coating system used for applying a coating composition to a web prior to printing. The method includes the steps of inserting a test fluid in a web coating. The test fluid includes water, a polyol, a surfactant, a radiant energy activated tracer compound and an organic solvent selected from the group consisting of an alkylene glycol and a dialkylene glycol. The test fluid is then applied to a web to provide a test fluid coating on the web and the web is exposed to a radiant energy source. Upon identification of deficiencies in the coating system, the coating system is adjusted to provide a substantially uniform coating composition on a web prior to printing.
As used herein, the term xe2x80x9cbleedingxe2x80x9d refers to the unintended mixing of colors or wicking of ink colorant into the web rather than remaining on the surface of the web. Webs which are highly absorbent of the colorant tend to produce low resolution images because each ink dot tends to spread due to the affinity of the web fibers for the colorants in the ink. If the ink colorant penetrates too far into the web, too much light may be scattered by the interstices of the upper portion of the web resulting in a lower contrast image. Accordingly, it is desirable that only the ink carrier be absorbed into the web while the colorant remains substantially on the surface of the web.
An important advantage of the invention is the use of a substantially colorless test fluid to readily identify deficiencies in the web coating system without printing multiple visible alignment indicia or visible test patterns on a coated web. Once such deficiencies are identified, adjustments may be made to the web coating system before assembling the coating system in an ink jet printer. The test fluid is also selected to be compatible with the coating composition used during a printing operation while at the same time being substantially colorless, relatively non-corrosive, and stable so that long term storage of the test fluid in the coating system does not harm the coating system. Other important advantages and benefits of the test fluid and method are included in the following detailed description thereof.